Difração de raios-X e espalhamento Raman nos cristais de CsxRbi_XLiSO4

Abstract

ln this work, we clid a study ofmixed crystal ofCsxRb1 _xLiSO4 , using the x-ray diffraction and Raman spectroscopy techniques at room temperature, within the interval of 0 $ x $ 1,0. We observed by x-ray diffraction 3 distinct crystal symmetries : monoclinic (O$ x $ 4,0), orthorhombic (0,70 $ x $ 1,00) and a new intermecliate symmetry (0,5 $ x $ 0,6). We studied the lattice parameter as afunction ofthe concentration in the monoclinic and orthorhombic symmetry by means ofx-ray powder diffraction using theRietveld method. Our experimental results were compared with those obtained by Katkanant using simulation oflattice dynamics and molecular dynamics theories. The identification off requencies and classification ofnormal modes of active vibration were done by Raman spectroscopy for monoclinic and orthorhombic symmetry. We analyze the influence of substitution Cs---. Rb in the monoclinic structure and Rb---.Cs in the orthorhombic structure by dynamics of SO42, responsible by mechanism of phase transition as a function of temperature. ln the intermediate symmetry, our results reject the Pietrasko 's propose of monoclinic structure belonging to the P21 (C5 2h) space group, which correspond to the RbLiSO4 between 455-475K . A set of possible space groups were obtained as strongest candidates to this structure based on the analysis of group theory ofRaman measurements using several polarizations and by extinction of observed reflection tookfrom x-ray powder cliffraction. The lattice parameters were obtained by x-ray diffraction using different programs: ITO andDICVOL91. Also, we observed a phase transition ofthis new crystal at low temperature between 102,5 - 290K using the x-ray low temperature camera.